Mechanical Engineering
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# Mechanical Numerical of the day : May 18 2021

## Question

A gear has to be shrunk on a shaft of basic size 120 mm. An interference fit H7/u6 is being selected. Determine the minimum and maximum diameter of the shaft and interference.

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Maximum dia of shaft : 120.166
Minimum dia of shaft : 120.144
Maximum interference : 0.166
Minimum interference : 0.109

A gear has to be shrunk on a shaft of basic size 120 mm. An interference fit H7/u6 is being selected. Determine the minimum and maximum diameter of the shaft and interference.

Maximum dia of shaft : 120.166

Minimum dia of shaft : 120.144

Maximum interference : 0.166

Minimum interference : 0.109

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Ans. 120.144 mm, 120.166 mm; 0.109 mm, 0.166 mm

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(https://www.mathcha.io/editor for writing these expressions)

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Max shaft dia. is 120.166mm / Interference -0.109

Min. shaft dia. is 120.144mm / Interference -0.166

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Upper limit of shaft- 178.58 mm.

Lower limit of shaft- 155.40 mm

Interference fit- 35.43 mm

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17 hours ago, Balaji Nidaganti said:

Upper limit of shaft- 178.58 mm.

Lower limit of shaft- 155.40 mm

Interference fit- 35.43 mm

My way of solving this problem would be to just "google it", since it's a problem described by a standard.
To be honest, I didn't look at the pictures, but I'll point out some errors:
- Imagine 3.5cm of interference on a 12cm diameter.
- Lower limit of a 12cm diametar shaft is 15.5cm

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1 hour ago, Marin Badurina said:

My way of solving this problem would be to just "google it", since it's a problem described by a standard.
To be honest, I didn't look at the pictures, but I'll point out some errors:
- Imagine 3.5cm of interference on a 12cm diameter.
- Lower limit of a 12cm diametar shaft is 15.5cm

Thank you....I found my mistake....I corrected it....

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Just perusing the answers to this quiz...I find them...well....."interesting" answers to say the least and...er.."worryingly" consistent. If the shaft starts at 120mm you need to think on the maximum size of the shaft available....are you going to spray-weld the shaft to increase its size...before you even begin?

If you look at the question it states the SHAFT diameter is 120mm....

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Posted (edited)
2 hours ago, G B Reid MIMechE, SIMarEST said:

Just perusing the answers to this quiz...I find them...well....."interesting" answers that say the least and...er.."worryingly" consistent. If the shaft starts at 120mm you need to think on the maximum size of the shaft available....are you going to spray-weld the shaft to increase its size...before you even begin?

If you look at the question it states the SHAFT diameter is 120mm....

Worryingly consistent is what I saw back at the 30mm chain link diameter. Thank you for the thought correction. Feeling ashamed now. Let me try solving:

All dimensions in [mm].
For 100-120:
Hole H7 ---> +0.000 - +0.035
Shaft u6 ---> +0.144 - +0.166
It's a really tight fit.

Assuming that max. shaft diameter is phisically 120mm:
d.max = 120.000
d.nom = 120 - 0.166 = 119.834
d.min = 119.834 - 0.144 = 119.690

Hole nominal size = shaft nominal size
D.nom = 119.834
D.min = 119.834 + 0 = 119.834
D.max = 119.834 + 0.035 = 119.869

If anyone has further insigtht, please correct this.
Edit: Also - thanks, admin, for presenting us with those problems. Love it when plain school thinking ain't enough.

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30 minutes ago, Marin Badurina said:

Worryingly consistent is what I saw back at the 30mm chain link diameter. Thank you for the thought correction. Feeling ashamed now. Let me try solving:

All dimensions in [mm].
For 100-120:
Hole H7 ---> +0.000 - +0.035
Shaft u6 ---> +0.144 - +0.166
It's a really tight fit.

Assuming that max. shaft diameter is phisically 120mm:
d.max = 120.000
d.nom = 120 - 0.166 = 119.834
d.min = 119.834 - 0.144 = 119.690

Hole nominal size = shaft nominal size
D.nom = 119.834
D.min = 119.834 + 0 = 119.834
D.max = 119.834 + 0.035 = 119.869

If anyone has further insigtht, please correct this.

Marin; NEVER feel ashamed for attempting something and making an error....being ashamed should be left to those who do not try - and I include myself in that (ie I have not tried and that IS shameful!!!).

I've been an Engineer now for 30 years, and the one thing I can say without fear of contradiction is you NEVER learn anything from getting things right...that just generates hubris...it reassures that the calculations are done correctly, but that can occur without the deepened understanding needed to be successful in the field!

Celebrate mistakes, especially if you learn from them!

And to tackle my "Shame":

Using the H7/u6 details on the quoted text (reference docs not available)

Generally on a "nominal" 120mm dia shaft, allow for a "runout" of 0.1, so all dimensions should be a minimum of the runout on both sides (120 - (0.1*2)) = 119.8 - ie the maximum diameter of the shaft MUST be below this value.

Therefore assuming a "base" of 119.6mm to allow for the +.166 of the shaft...

Therefore shaft at u6 = 119.744 - 119.766 (on a "base" of 119.6mm - +.144+.166)

Hole on H7 = 119.6 - 119.635 (on a "base" of 119.6 - +0.000/+.0.035)

It's definitely an interference fit...now, where did I leave the nitrogen...?

I may be wrong; I look forward to Saurabh's answers!

Warmest wishes!

Bruce

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